1. Technical Field
The present invention generally relates to a variable gain amplifier, and more particularly to a wide-band variable gain amplifier with a clipping function.
2. Background Art
The ultrasound system has become an important and popular diagnostic tool due to its non-invasive and non-destructive nature. Modern high-performance ultrasound imaging diagnostic systems and techniques are commonly used to produce two- or three-dimensional images of internal features of patients.
An ultrasound system generally uses a probe containing an array of piezoelectric elements to transmit and receive ultrasound signals. The ultrasound system forms an image of human internal tissues by electrically exciting transducer elements to generate ultrasound signals that travel into the body. Echoes reflected from tissues and organs return to the transducer element and are converted into analog electrical receive signals (hereinafter referred to as “analog receive signals”). The transducer elements may output low amplitudes of the analog receive signals. Thus, the amplitudes of the analog electrical receive signals should be pre-amplified. Pre-amplification is carried out by a pre-amplifier installed on an output terminal of the transducer elements.
When the ultrasound signals are propagated into the tissues of the target object, their amplitude is attenuated. Thus, the attenuation of the ultrasound signals has to be compensated so as to obtain an accurate ultrasound image. Compensation may be achieved by adjusting the gain of the pre-amplified analog receive signals. The gain of the analog receive signals is usually adjusted by a variable gain amplifier.
The compensated analog receive signals are inputted into an analog-to-digital converter (ADC) for digital processing. That is, the analog receive signals are converted into digital receive signals by the ADC. Subsequently, receive-focusing and digital signal processing are carried out upon the digital receive signals to thereby form ultrasound image data.
Further, the analog receive signals may be amplified by the variable gain amplifier beyond an amplitude range allowable for input to the ADC by the variable gain amplifier. If the analog receive signals are amplified beyond an allowable amplitude range as an ADC input or a recovery time is increased due to overload, the ADC may malfunction so that an accurate ultrasound image signal may be not obtained. Thus, a wide-band variable gain amplifier capable of outputting amplified analog receive signals within a limited amplitude range is needed.